Irrigating in the zone

In 2010, J.J. Long joined the small but emerging variable-rate irrigation club to manage a pivot circle with “wildly varying soil types.” Half of the circle seldom reached his yield expectations. “It never seemed to get enough water,” he says.

He believes he’s fixed that yield challenge by equipping the pivot with a CropMetrics precision ag package for VRI. It was one of 100 systems in Nebraska and Kansas last year varying water rates based on a VRI prescription generated by a new agronomic tool.

Long, who farms near Grant, intends to add the program to two additional pivots this season. “I basically have irrigated by the ‘guess method,’” he says. “My goal now is not uniform water application, but uniform yield instead by matching the water rates to soil types and their water-holding capacities.”

He accomplishes this by delivering the VRI prescription, generated by what CropMetrics calls its Virtual Agronomist (VA) software program, to a GPS-based AgSense Field Commander remote controller installed at the pivot’s end tower. The water prescription is wirelessly transmitted from the VA program to the AgSense unit that ultimately controls the pivot’s variable speed.

At a glance

Variable-rate irrigation may conserve water and raise yields.

CropMetrics service divides the field in different zones.

The irrigation service is provided through agronomists and consultants.


VRI speed control varies irrigation application rates in up to 60 different management zones, or pie slices, in the circle by speeding up or slowing down the pivot, says Kevin Abts, head of CropMetrics sales and marketing.

To create the water prescription, the VA software automatically analyzes the soil types and water-holding capacities, field topography and yield data. Long also installed a soil moisture probe in an area determined by the VA program as representative of the field’s overall majority soil type, and he relies on the probe’s reading to determine both the optimal base application rate and exactly when to irrigate.

“Then the water prescription determines how to vary the rates. If I decide to apply a base rate of an inch of water, the pivot may apply 0.80 to a wetter zone and 1.20 inches to a drier zone,” he says.

In Long’s case, the VA program uses high-resolution soil maps in the form of data layers to create prescriptions that slow down the system over sandy soils to deliver more water and speed it up over heavier clay-type soils that have a higher water-holding capacity.

Crafting a prescription

Building the water prescription with the VA program is the foundation of CropMetrics. Nick Emanuel of North Bend, company president, says three categories of information are collected and layered: an EM (electromagnetic) survey of the field to map soil types and water-holding capacities, an RTK elevation map of field topography, and yield history for at least three years. The EM survey is made with an implement pulled through the field by an all-terrain vehicle.

CropMetrics contracts with Midwest Independent Soil Samplers, a Minnesota company, to make the EM and field topography surveys.

“We come up with site-specific yield optimization opportunities,” Emanuel says. “With our program, the data is available for not only variable-rate irrigation, but also VR seeding and nitrogen.”

The majority of CropMetrics pivots in 2010 were outfitted with the Field Commander, a GPS-based, remote-telemetry unit from a South Dakota company called AgSense. The unit receives prescriptions created by the VA program and then automatically relays them to the pivot.

CropMetrics markets its VA program to agronomists and crop consultants who are trained and certified as VRI specialists, and they in turn offer it to farmers as part of their precision ag services.

Costs for a three-year CropMetrics program is $8 an acre per year. For more information, go to www.cropmetrics.com.

It’s about more than saving water

Today there is a flood of newer irrigation technologies that are generally designed to help farmers save irrigation water. J.J. Long says he reduced overall water output only slightly on his CropMetrics-outfitted center pivot in 2010 vs. an adjacent pivot with the same general terrain, variable soil types and corn hybrid, but he yielded 15 bushels more per acre by making the water application more efficient and productive.

“The hillsides yielded better than they ever had because the irrigation application rates were better managed,” Long says. “It’s not necessarily about reducing overall water, but about more uniform moisture and yield.”

Long farms within the Upper Republican Natural Resources District, which sets a per-year pumping allocation for irrigators. He says it will be easier to stay within those limits with variable-rate irrigation. “I can move more quickly over wetter areas of the field.”

As he learns this new approach, Long says the program has him thinking more about irrigation efficiency beyond the center pivot. “I may have my pump tested for performance, and I’m considering changes in my sprinkler packages.”

This VRI even more precise

Valley Irrigation’s new VRI Zone Control technology provides individual sprinkler or span control, says Jake Larue, company product manager.

As part of a recent partnership agreement, Valley uses the CropMetrics VRI Optimization service to design water prescriptions for VRI Zone Control. Valley has the control panels and other hardware to vary irrigation rates at any point along the pivot span, but it lacked the agronomic program to generate the prescriptions.

In addition to adjusting the pivot speed, VRI Zone Control delivers variable water rates via individual sprinklers or banks of sprinklers, allowing for more and smaller management zones. The company says its VRI Zone Control is compatible with new and existing pivots of any brand equipped with the Valley Irrigation Pro2 control panel. With Valley VRI Zone Control, up to 5,400 different management zones are possible in a circle.

However, because of the need for additional VRI control boxes, valves and hoses, it costs more than the VRI Speed Control option. CropMetrics provides a cost-benefit analysis of VRI Speed Control vs. VRI Zone Control for every field.

The partnership between CropMetrics and Valley Irrigation allows the Valley dealer network to market the CropMetrics VRI Optimization service.

Prescription for variable rates

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WATER RAINBOW: The right-hand circle shows the variable-rate irrigation water prescription for a pivot circle. For example, the system would slow down over the yellow and red pie slices, most likely sandy soils, to deliver more water. The other colored circle represents the soil types and water-holding capacities as determined by an electromagnetic soil survey.

This article published in the March, 2011 edition of NEBRASKA FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.